To date, it has been known that, by applying a power storage device, such as a secondary battery or an electric double layer capacitor, to an electric railway system so as to configure the electric railway system in such away that superfluous regenerative electric power generated while the vehicle is braked (during a regenerative period) is stored in the power storage device and the stored electric power is utilized while the vehicle is accelerated (during a power running period), the kinetic energy of the vehicle can effectively be utilized (e.g., Non-Patent Document 1).
[Non-Patent Document 1]
    Institute of Electrical Engineers of Japan, national convention 5-176, 2005, “Development of Power Storage System for DC Rolling Stock applying Electric Double Layer Capacitor”
A smallest element of a power storage device utilized for the power storage system is referred to as a cell and a plurality of cells connected in a series-parallel fashion is referred to as a module. A necessary voltage and a necessary current are obtained by further connecting a great number of the modules.